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histology
the study of tissues
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tissue
an aggregation of cells
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epithelial tissue
- tightly packed and tightly connected cells
- come from all three germ layers
- simple, stratified, or pseudostratefied
- covers outside of body, internal organs, body cavities
- anchored to connective tissue by a basement membrane
- functions - protection against bacterial invasion, fluid loss, mechanical damage; secretion, excretion, sensory reception, absorption
- ciliary movement sweeps material across the surface of the epithelium
- no direct blood supply; diffusion of gases
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simple epithelium
one cell layer
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stratified epithelium
composed of multiple layers
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pseudostratified epithelium
consists of one layer, but location of nuclei makes it seem that there are multiple layers
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basement membrane
extracellular matrix secreted by epithelial cells that separates these cells from the connective tissue
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simple squamous epithelium
- single layer of thin or flattened cells
- "leaky"; allow for diffusion of gases across their surfaces or between adjacent cells
- found in capillaries, veins, arteries
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simple cuboidal epithelium
- single layer of cube-shaped cells
- carries out secretion and absorption
- found in kidney tubules and various glands
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simple columnar epithelium
- elongated, column-shaped cells
- nuclei are located near the basement membrane
- involved in absorption
- line the uterus and digestive tract
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stratified squamous epithelium
- composed of many cell layers
- covers the skin and lines the mouth, throat, vagina, anal canal
- includes keratin fibers
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keratin
- protein fibers
- found in skin cells, nails, hair
- waterproof; protects the skin against microbial invasion and injury
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pseudostratified columnar epithelium
- single layer of cells
- location of the nuclei differ from cell to cell, so the tissue takes on the appearance of multiple cell layers
- line the trachea and respiratory tract
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glandular epithelium
- specialized to secrete substances
- found in most glands; mammary, sweat, endocrine glands
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connective tissue
- connects, supports, protects other tissues; fills space, produces blood cells, provides protection, repair damaged tissues
- sparse population of cells inside an extracellular ground substance
- fibers (made of primarily collagen)
- ground substance consists of different noncollagenous proteins, water, salts, metabolites, etc.; vary from fluid to solid
- mesodermal origin
- no direct blood supply; diffusion
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loose connective tissue
- binds epithelia to underlying tissues
- forms the membranes between organs; beneath the skin
- composed of spindle-shaped cells (fibroblasts) that produce the fibers
- some immune cells (macrophages) are present
- made of collagen fibers and elastin fibers
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collagen fibers
give strength to resist stretching
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elastin fibers
flexible, allow for some distortion
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adipose tissue
- stores fat (energy storage), cushions organs and joints, insulates
- found beneath the skin, in abdominal membranes, around the brain, heart, kidneys, and joints
- lipids are stored in a large vacuole, called a fat droplet
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fibrous connective tissue
- often binds different materials together
- found in tendons, ligaments, whites of the eye, and deep layers of the skin
- composed mostly of strong collagen fibers and relatively few cells
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tendons
connect muscle to bone
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ligaments
connect bone to bone at joints
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cartilage
- provides support and a framework for various body parts
- retained in the trachea, vertebral column, ears and nose, and ends of some bones; bone typically replaces most cartilage in vertebrates
- chondrocytesare present in small island-like cavities called lacunae
- composed of collagen fibers and a gel-like ground substanct
- does not have a blood supply
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bone
- protects vital organ and provides a tough endoskeleton for bones to work against, stores vital ions (calcium and phosphate), main site where blood cells are produced (in the marrow)
- collagen fibers and cells (osteocytes) in a hardened matrix filled with calcium phosphate salts
- fibers help bone to resist tensile forces; matrix resists compression
- strongest connective tissue
- osteocytes are found in lacunae
- arranged in concentric circles (lamellae) around Haversian canals (containing the blood vessels and nerves); small canaliculi (canals) are observed sticking across the lamellae
- osteons are the fundamental unit of bone
- includes osteoblast and osteoclast cells
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osteoblast
- uninucleated cells that produce bone
- become mature osteocytes when encased in the bone
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osteoclast
large, multinucleated cells that tear down or reabsorb bone
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blood
- transports substances and helps maintain homeostasis
- consists of cells in a watery matrix (plasma), erythrocytes, leukocytes, and platelets
- fibers can form if blood clotting is stimulated to form the fibrin blood clot
- proteins include - fibrin[ogen], globulins, albumins
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erythrocytes
- red blood cells
- contain hemoglobin for oxygen transport
- anucleated when mature
- biconclave - a thin membrane is stretched across the center, making the cell very distortable
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leukocytes
- white blood cells
- involved in immune responses
- produces anitobies, toxic chemicals, use phagocytosis
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platelets
fragments of cells involved in blood clotting
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muscle tissues
- most abundant type (in terms of weight)
- elongated cells that are capable of contraction upon stimulation
- mesodermal origin
- contain many parallel bundles of microfilaments made of actin and myosin
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skeletal muscle
- voluntary control
- striated
- multinucleated
- large cylindrical cells
- cells (muscle fibers) are grouped into muscle bundles, which are grouped into muscles
- metabolically active; vascularized
- attached to bones by fibrous connective tissue called tendons
- contract and fatigue most rapidly
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smooth muscle
- cells are long and spindle-shaped
- no striations
- uninucleated
- found in the walls of hollow internal organs
- involuntary control
- contract and fatigue slowly
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cardiac muscle
- found only in the heart
- involuntary control
- adapted to rhythmic contractions
- single nuclus
- striated
- cells are often branched
- cells are connected by intercalated disks; structures help to coordinate contraction
- intermediate in terms of fatigue and contraction speed; cells rest between heartbeats
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nervous tissues
- found in the brain, spinal cord, and peripheral nerves
- sense external and internal stimuli
- send signals; function in coordinating, regulating, and integrating body activities
- of ectodermal origin
- send action potentials in a unidirectional direction (from presynaptic cells to postsynaptic cells)
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effector organs include:
glands and muscles
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neuron
- basic type of nerve cell
- uninucleated
- consist of a soma (cell body), axon (sends), and one or more dendrites (recieves)
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glial cells
supportive cells in nervous tissue
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